Full-scale anaerobic digestion optimisation study
A full scale-study was undertaken on anaerobic digestion of municipal wastewater sludge in Collingwood, Ontario to determine if improvements in biogas production, pathogen reduction and sludge quality were possible at 44°C versus conventional mesophilic digestion at 35°C. Two HRTs were to be tested (20 and 40 days), as well as series operation of the digestion process, with one or both digesters at 35°C and 44°C and employing equal HRT in each digester. Technical difficulties meant that only two of the single-stage trials at 20 days HRT were completed, at 35°C and 44°C. They showed no statistically significant difference in average gas production, at 1031 m3/d for 35°C and 1035 m3/d at 44°C. Sludge quality was improved at 44°C in terms of fecal coliform reduction, but was not statistically significantly different for other pathogens (fecal streptococcus, ' E.coli' and 'Salmonella'), nutrient content and dewaterability. Pathogen reduction ranged from 1.1 to 3.3 log reduction at 44°C and 1.0 to 2.5 log reduction at 35°C.